352 Description of an improved Reflecting Circle. 



screw, which will move the index a small quantity when 

 turned, to adjust it accurately; G is the index mirror 

 screwed upon the index 11, which has also a vernier, and a 

 clanip i\u\ tangent screw ee, similar to the other; I is the 

 handle by which tl^e instrument is held when in use; ii is 

 fitted to a socket K, which is screwed to the centre oK the 

 circle, and is unscrewed from the circle when packed away; 

 the handle is (iitcd to a springing socket, so as to turn round 

 upon the socket K, that it may l)e turned to any side of the 

 circle fyr the convenience of holding it ; it may be fastened 

 bv a small milled nut, seen in the figure which binds the 

 ends of tlie sprin<r socket together; L is a magnifying 

 gLiss fur th.e purpose of reading the divisions of the ver- 

 niers ; it is fitted upon a pin sciewed into the indexes, and 

 may be applied to either. The figure 2 in llie corner of the 

 plate is a section, showing the construction ot the central 

 part of the circle, where M is a section of the thickness of 

 the circle with a hole through the centre, and a recess turned 

 out in the lower side to receive a centre-piece N, which is 

 fixed in with three Small screws; a hole is turned in the 

 centre of this piece, and an axis O is fitted into it with the. 

 utmost accuracy, this axis has a flanch on the upper end by 

 which it is screwed to the index H, and upon this, the un- 

 der glass G, fig. 1, is fastened, by other screws passing 

 through a piece projecting from the back of it ; the axis is 

 held in its place by a collet r, fitted on a square part of it, 

 and held fast by a screw ,$•; beneath' this a piece is fixed on 

 in the centre of the circle, the edge of its tlanch being 

 shown by t in fig. 1, it is part of the screw which holds on 

 the spring-socket K, for the handle I, the upper end of the 

 centre- piece N which comes up above the circle, is turned 

 extremely true, and upon this the index B is fitted, or 

 rather a brass ring v screwed to it, so as to turn round upon 

 it as a centre. 



The telescope C, is fixed to the index by two cocks and 

 by two screws xx, in these it can be raised up or lowered, 

 to adjust the different brightness of the two objects seen in 

 the horizon- glass D, the one reflected from the central 

 mirror G, and the other seen directly through it; the dark 

 glasses at E, are intended to moderate the light of the sun, 

 in passing from the index to the horizon -glasses ; the frames 

 c<mtaininii these szlasses have holes E throuoh them, to see 

 throu<rh the telescope and horizon-glass, the other dark 

 classes F, arc situated behind the horizon-glass D, and may 

 be turned up or down as occasion requires. 



The instrument is used in the same manner as the com- 

 mon 



